In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, dust particles, sometimes referred to as fly ash. The dust particles are often removed from the process gas by means of an electrostatic precipitator, also called ESP, for instance of the type illustrated in U.S. Pat. No. 4,502,872.
A combustion plant normally comprises a boiler in which the heat of the hot process gas is utilized for generating steam. The boiler comprises internal heat transfer surfaces which become gradually fouled by dust particles of the process gas. To maintain a high heat transfer capacity the boiler is occasionally soot-blown by means of, e.g., blowing steam onto the internal heat transfer surfaces to remove the dust particles collected on the heat transfer surfaces. The removed dust particles leave the boiler together with the hot process gas. Thus, the concentration of dust particles in the hot process gas is increased during the soot-blowing procedure.
JP 62201660 in the name of Mitsubishi Heavy Industries describes a method of cleaning a hot process gas generated in a boiler. An electrostatic precipitator, ESP, is operative for removing dust particles from the hot process gas. During the soot-blowing of a gas-heater an increased amount of dust particles must be removed from the hot process gas. In accordance with JP 62201660 the ESP can operate in two different modes, a first mode, to be used during soot-blowing of the gas heater, in which first mode a power source provides maximum charge to the electrostatic precipitator, and a second mode in which the power source provides a lower charge, to be utilized between soot-blowing sequences.
While the method of JP 62201660 may in some cases decrease the amount of dust particles emitted during soot-blowing of the ESP it also results in a higher energy consumption, and requires a power source which is able to operate at a higher charging rate than what is useful in normal operation.